This week I’ve made a small change in the format of the article. This week I wanted to write in depth about the history and science behind one particular food. I hope you find this as fascinating as I do. We will return to the kitchen next week and make some sweet treats.
There was a secret formula so dear that Charles I was reputed to have offered his French chef a five hundred pound pension just to secure it. Today it’s available in your grocer’s freezer. Ice cream, like gelatin, took a long and interesting journey from the exclusive tables of the rich to the corner store. Science had to solve some fundamental problems before the product could be sold at prices accessible to everyone.
Before mechanical refrigeration it would have been difficult to freeze a solution of milk and sugar. The temperature required is much lower than can be achieved by packing it in snow or in an ice and water slush. By the 13th century it was known in the Arab world that salt would lower the temperature of ice. In the west, it wasn’t until 1589 in Naples that Gaimbattista Della Porta froze a glass of wine which he buried in salt and ice.
In May, 1671 we know that ice cream was served at a dinner by Charles II; but it was only served to the head table. Shortly after recipes resembling ice cream began to appear in print. Niege de Fleurs d’Orange, in The Nouveau Confiturier (1682) and Fromage a l’Angloise, from Massialot’s La Novelle Instruction pour les Confitures (1692). These recipes froze the product without stirring so the resulting ice cream would be very dense, with almost no air incorporated. By the late 1700’s though, the French had discovered that frequently stirring the mix as it cooled produced a lighter product with a finer grain and smaller crystals. The innovation quickly spread, we would easily recognize the ice creams that both Washington and Jefferson enjoyed serving at state dinners.
The next big advances in ice cream retailing both occurred in the mid 1800’s in America. In 1843, Nancy Johnson, of Philadelphia, patented and marketed the familiar barrel shaped ice cream maker. Her design consisted of two paddles set in a cylinder that rotated inside of a barrel that was filled with ice and rock salt. Home ice cream makers today are virtually unchanged, though now chemical coolants have replaced the salt and ice. In 1850, Jacob Fusell, a dairy farmer near Baltimore, used Johnson’s design and his seasonal surplus of cream to begin the first large scale production of ice cream. Fusell was able to charge prices less than half the rate of the specialty shops where ice cream was normally marketed and ice cream became a common food in America. An English visitor, in 1890, was so struck by “the enormous quantities” of ice cream he saw consumed he felt he needed to include this observation in a letter home. In the 1950’s, when freezers were introduced in most homes, ice cream’s takeover of America was complete. Today the world market for Ice Cream is 14.4 billion liters; about 2.4 liters per person. In the US, our consumption is reported at 22 liters per person. Nine percent of US milk production goes into the production of ice cream.
Before going into the kitchen to make ice cream it would be beneficial to take a close look at ice cream to understand what the ingredients and techniques are trying to do. In Introduction to Food Colloids, professor Dickinson calls ice cream “just about the most complex food colloid of all”. Ice cream contains matter in all three states. Ice crystals (a solid) and air (a gas) are held together in a continuous liquid phase of sugar and water known as the matrix. A colloid is a substance where a small part of matter in one state are held in a continuous phase of some other matter (often, but not always, in another state). Typical ice cream is made up of 30% ice crystals, 50% air bubbles, 5% fat droplets all less than .1mm in diameter held in continuous 15% liquid matrix made up of sugar, water, and some milk proteins. Ice cream exhibits the properties of three types of colloids: the fat held in water called an emulsion, the ice held in water called a sol, and the air held in water called a foam. When following proper technique to make ice cream we are creating these three colloids.
Earlier we learned one of the challenges that ice cream makers had to overcome was how to freeze a sweet mixture of cream and sugar because it froze at a temperature colder than ice or snow. This same principle is what helps to form the matrix. If we were too slowly freeze a glass of water, taking it’s temperature along the way, we would observe that the temperature would fall steadily to zero degrees Celsius, as you might expect. But it will continue to fall a short distance below zero degrees before we see ice forming and the temperature of our glass of water jumps rabidly up to zero and stays there. This is because the water molecules, who want to form into neatly organized six sided crystals, need to find a like seed crystal to form onto. In pure water there is nothing to form onto so they continue to search for a short time before enough random crystals meet to form the ice. The water gains some energy when ice crystals finally form because below zero degrees ice has less energy than water. The difference between zero and the point ice forms is known as super cooling. When a solute, like sugar or salt, is present it gets in the way of the ice crystals as they try to form their neat hex-shaped lattice. The freezing point is lowered and there is increased super cooling before ice is formed. More importantly, in making frozen desserts, the ice crystals that do finally form take available water out of the solution. This increases the concentration of the solutes and further lowers the freezing point. Therefore, at the temperatures we can achieve in the kitchen, there will always be a mix of sweet sugar water and ice crystals in our frozen desserts.
Because of their powerful effect on freezing points sugars do more than make the resulting dessert sweet. They also control the amount of ice in the final product and affect the viscosity of the final matrix. This is also one of the reasons ice creams should be tempered before serving. The normal freezer operates near zero degrees Fahrenheit. At 10F the ice cream will no longer numb the mouth and it will have more water in the matrix. By 22F half of the ice will be converted into water. More water means a softer smoother texture.
The fats in ice cream, from the cream primarily, slow the rate the ice cream melts. Fat transfers some flavors and smells that dissolve easier in fat than water. The primary purpose though is to stabilize the foam. We can think about a familiar foam, whipped cream, to help illustrate. When the whisk is passed through the cream large air bubbles pass through the cream. With each pass of the whisk, more bubbles are added and the existing bubbles are broken into smaller bubbles. The cream forms a film around the bubbles of air keeping them from coming back together. The viscosity of the liquid is what is important here. Too thick and you can’t incorporate air, like whipping caramel. Too thin and the film is not strong enough to keep the air bubbles apart. This is one reason you can’t make whipped water. Stabilizers are used to keep the bubbles intact. Commercially these would be mono and diglycerides. At home we use the lecithin in egg yolk. These stabilizers work because they are long molecules with a unique property, one side of them prefers to be in water and one side repels water. The glycerol ‘head’ is hydrophilic and will seek out water. The fatty acid ‘tail’ is hydrophobic and will grab on to the fat. Now we can picture an air bubble coated in a film of fat and zippering it into the matrix are the stabilizers with their heads in the liquid matrix and their tails firmly in the film of fat.
The air trapped in the foam makes the ice cream lighter and less dense. While some air is necessary to achieve the desired texture too much is considered poor quality. Premium ice creams sold in the supermarket have less air than cheaper ice creams. Air is measured by the term overrun. Overrun is defined as the quantity of the volume of the ice cream minus the volume of the mix divided by the volume of the mix. Overruns can be up to 100% in economy ice creams this means the mix they used doubled in volume before it was packed. Premium ice creams tend to fall between 20-40% while ice creams made at home rarely top 20%. The term ‘premium’ is not a regulated term and has no guaranteed meaning on a pack of ice cream. But because ice cream is sold by volume not by weight you can get a general idea of quality by hefting the packages. Better ice cream should be denser, heavy in relation to the size of its package.
Now that we’ve taken some time to look over the history of Ice Cream, it’s composition, and the importance roles of its ingredients there is one more topic to discuss before heading to the kitchen. Let’s look at the taxonomy of ice cream and identify the differences between the various frozen desserts.
Ice cream is a blend of milk, and sugar frozen with the addition of air. In the US ice creams must be at least 10% fats and 20% milk solids to be marketed as ice cream. There are two principle distinctions to make when talking about ice cream. ‘Philadelphia’ ice cream is the standard ice cream. It is made from milk, cream and sugar and may contain inclusions of fruit, nuts, vanilla, or chocolate. The benefit of Philadelphia ice cream is the clean flavor of the cream and the inclusions. ‘French’ or ‘Custard’ ice creams often taste richer but because they are made with egg yolks (as many as 12/lt) they can be made without cream, and only less expensive milk. Because they contain eggs the mix must first be cooked which alters the flavor of the milk. The eggs also add a distinct flavor which many people find desirable. French ice creams are the ones most often prepared in the home. The egg yolk helps to stabilize the mixture and control the growth of ice crystals making it a very forgiving technique once the cook has mastered making the custard base. ‘Gelato’ , which means ‘frozen’ in Italian is a rich form of custard ice cream. It is made with a high amount of butterfat, from cream, and has a low overrun (10% or about half of French Ice creams) producing a rich dense product.
Sorbetto and Sorbet are made from mostly fruit juice (up to 80%) with sugar, water, flavorings and sometimes even alcohol added. They are agitated while freezing to produce fine smooth crystals. Plant fiber from the juice used can also help control ice growth. Sherbets are sorbets with the addition of milk or cream. Popular in fancy restaurants as an intermezzo, Granita is a sorbet that is frozen quiescently, that is without agitation. It is characterized by large, often flat crystals in a flavored syrup. Water Ices are also similar to sorbets but by definition contain no fruit juice. They are frozen sugar syrup with flavoring and color added. If they do contain any fruit juice they are properly called fruit ices.
Kulfi, an Indian Ice cream deserves special mention. Kulfi is made by quiescently freezing milk that has been cooked down till only a little remains. This greatly concentrates the milk sugars and proteins and takes away a large part of the water that is naturally part of the milk. It has a strong flavor of the cooked milk and a butterscotch like color and taste.
Maras is a traditional Turkish Ice cream preparation. It is made by adding Sahlep, and ingredient derived from the tubers of a certain orchid. The sahlep, a long polysaccharide, interacts with the milk proteins to create a uniquely elastic, stringy texture in the resulting ice cream. I’ve found sahlep in Philadelphia sold as a drink mix and am looking forward to trying to create this treat at home.
I hope you enjoyed this close look at a summer treat. If you want to learn even more on this interesting topic I recommend Chris Clarke’s book The Science of Ice Cream. I also find Harold Magee’s On Food and Cooking indispensable for all my food questions. Next week we will return to the kitchen and make some ice cream for ourselves. Till then Happy Cooking
